Question

A student carries out an experiment to investigate the role passive transport plays in maintaining homeostasis in organisms. For this investigation, the student uses two gummy bear candies to represent animal cells. The student records the mass of each bear. Then, he places one in a beaker filled with distilled water. He places the other in a beaker filled with salt water. After 48 hours, he removes the bears from the beakers and records their masses again. He finds that the mass of the gummy bear in the distilled water significantly increased, while the mass of the gummy bear in the salt water significantly decreased.

Which of the following is the best interpretation of the observations made during the investigation?

A.
Distilled water was able to stick to the surface of the gummy bear when it was removed from the beaker, while the salt water was not.

B.
Distilled water was able to be absorbed by the gummy bear, while the solute in the salt water prevented the movement of water.

C.
Salt entered or left the gummy bears so that the concentration of solute would be equal in the solution and in the gummy bears.

D.
Water entered or left the gummy bears so that the concentration of water molecules would be equal in the solution and in the gummy bears.

Answer 1

D.

The mass changes are explained by osmosis: water moves passively from regions of higher water concentration (distilled water) to lower concentration (inside the gummy bear), so the distilled-water bear swells. In salt water (lower external water concentration), water leaves the bear, so its mass decreases.